A planar optical waveguide typically comprises a substrate, composed of a relatively low index of refraction dielectric material, supporting a planar layer of a relatively high index of refraction dielectric material. To couple a light beam propagating in an optical fiber into the planar optical waveguide there must be proper phase matching of the evanescent fields of light beams propagating in the optical fiber and the planar waveguide. Hammer, in U.S. Pat. No. 3,912,363 issued Oct. 14, 1975, entitled OPTICAL FIBER TO PLANAR WAVEGUIDE COUPLER and assigned to the assignee in the present application, has disclosed that the proper phase matching of the evanescent fields is enhanced by the use of a relief phase grating situated in the surface of the planar layer in close proximity to the coupling end of the optical fiber. The grating may be holographically recorded in the photoresist layer overlying the planar layer or produced in the planar layer by ion beam milling. A blazed grating, one having an asymmetric groove structure, is preferred since it will provide improved coupling efficiency between the optical fiber and the planar waveguide. Blazed gratings have been formed in a surface by masking of the surface and subsequent ion milling of the surface with the substrate oriented at an angle to the particle beam. Asymmetric grooves are then formed due to the shadowing effect of the masking layer on the particle beam. This method requires accurate deposition of the appropriate mask and subsequent accurate alignment of the surface to the particle beam. It would be desirable to have a method for the formation of a blazed grating which combine the simplicity of formation of a holographic grating in a light sensitive material with the ion milling technique which produces a grating in the planar layer itself.